For a hydraulic structure, seepage is one of the key factors affecting its safety service. To strengthen the effective sensing of seepage property is of great significance to find out the safety hazards in time and ensure the reliable operation of the hydraulic structure. With the development of a distributed optical fiber sensing technology, it has become an important research direction in the field of engineering safety like water conservancy and civil engineering to obtain the property information of the structure and sense the health conditions of the structure. However, there are still many technical problems that need to be solved and improved due to the particularity of the working environment and structural characteristics in the actual application of hydraulic structure seepage property distributed optical fiber sensing engineering.
First of all, when a sensing optical fiber is used for seepage monitoring, external circuits are usually needed to heat the optical fiber at current, and there are defects on such aspects like poor resistance to pressure and coordination deformation, and low seepage sensitivity. Therefore, it is desirable to sufficiently consider the characteristics of hydraulic seepage monitoring and special working environments, focus on the production and assembly of the sensing optical fiber itself, and develop a special optical fiber for seepage monitoring having an automatic control heat source, so as to improve the performance index and practical ability of the optical fiber seepage measurement technology. In addition, the most commonly used distributed optical fiber temperature sensing technology for indirectly sensing structure seepage property uses anti-Stokes Raman scattered light as a temperature measuring signal, uses a laser single pulse as a pump signal, and uses Stokes Raman scattered light as a temperature measurement reference channel But it has the defects of uneasily adjusted pulse width, low spatial resolution, and poor signal to noise ratio.
Secondly, in the application of monitoring a sensing optical fiber longer than 100 meters, only one or a few segments of the optical fiber are calibrated at present on the basis of segmentation calibration, with the average value of the temperature coefficient of the segment selected as the temperature coefficient of the entire sensing optical fiber. The precision will be constantly reduced with the increase of the length of the sensing optical fiber, and the method has the disadvantages of low calibration efficiency, short calibration length, low load weight, difficulty in cooling and cooling, and uneasy control of temperature. The long-distance wide-range effective calibration problem becomes one of the important obstacles to apply and promote the distributed sensing technology in hydraulic structure seepage property sensing in large scale.
Thirdly, in actual engineering application, the monitoring precision of the laid optical fiber is often reduced or the measured value is seriously distorted, and can't even be obtained since improper bending occurs or a bending section does not be effectively protected. Improper laying of the optical fiber causes the optical fiber to be not in conformity with the size and construction requirements of engineering structure and results in wastes. The laying of the sensing optical fiber, and especially the reasonable adjustment and control of the bending curvature radius of the optical fiber has become an important technical problem that affects the monitoring precision, service life and construction progress, etc. It is desirable to develop a device and a method for optical fiber bending curvature controlling and measuring with strong adaptability and operation accessibility, so as to reduce dependency on laying personnel, improve the survival rate for laying the optical fiber, prolong the service life of the sensing optical fiber, and sense dam property more effectively and accurately.